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SubjectRe: [PACTH v1] mm, proc: Implement /proc/<pid>/totmaps
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On 2016-08-10 11:02 AM, Jann Horn wrote:
> On Wed, Aug 10, 2016 at 10:16:45AM -0400, Robert Foss wrote:
>>
>>
>> On 2016-08-09 06:30 PM, Jann Horn wrote:
>>> On Tue, Aug 09, 2016 at 05:01:44PM -0400, Robert Foss wrote:
>>>> On 2016-08-09 03:24 PM, Jann Horn wrote:
>>>>> On Tue, Aug 09, 2016 at 12:05:43PM -0400, robert.foss@collabora.com wrote:
>>>>>> + down_read(&mm->mmap_sem);
>>>>>> + hold_task_mempolicy(priv);
>>>>>> +
>>>>>> + for (vma = mm->mmap; vma != priv->tail_vma; vma = vma->vm_next) {
>>>>>> + struct mem_size_stats mss;
>>>>>> + struct mm_walk smaps_walk = {
>>>>>> + .pmd_entry = smaps_pte_range,
>>>>>> + .mm = vma->vm_mm,
>>>>>> + .private = &mss,
>>>>>> + };
>>>>>> +
>>>>>> + if (vma->vm_mm && !is_vm_hugetlb_page(vma)) {
>>>>>> + memset(&mss, 0, sizeof(mss));
>>>>>> + walk_page_vma(vma, &smaps_walk);
>>>>>> + add_smaps_sum(&mss, mss_sum);
>>>>>> + }
>>>>>> + }
>>>>>
>>>>> Errrr... what? You accumulate values from mem_size_stats items into a
>>>>> struct mss_sum that is associated with the struct file? So when you
>>>>> read the file the second time, you get the old values plus the new ones?
>>>>> And when you read the file in parallel, you get inconsistent values?
>>>>>
>>>>> For most files in procfs, the behavior is that you can just call
>>>>> pread(fd, buf, sizeof(buf), 0) on the same fd again and again, giving
>>>>> you the current values every time, without mutating state. I strongly
>>>>> recommend that you get rid of priv->mss and just accumulate the state
>>>>> in a local variable (maybe one on the stack).
>>>>
>>>> So a simple "static struct mem_size_stats" in totmaps_proc_show() would be a
>>>> better solution?
>>>
>>> Er, why "static"? Are you trying to create shared state between different
>>> readers for some reason?
>>>
>>
>> I think I'm a bit confused now, how are you suggesting that I replace
>> priv->mss?
>
> Like this:
>
> static int totmaps_proc_show(struct seq_file *m, void *data)
> {
> struct proc_maps_private *priv = m->private;
> struct mm_struct *mm;
> struct vm_area_struct *vma;
> struct mem_size_stats mss_sum;
>
> memset(&mss_sum, 0, sizeof(mss_sum));
>
> [...]
>
> for (vma = mm->mmap; vma != priv->tail_vma; vma = vma->vm_next) {
> struct mem_size_stats mss;
> struct mm_walk smaps_walk = {
> .pmd_entry = smaps_pte_range,
> .mm = vma->vm_mm,
> .private = &mss,
> };
>
> if (vma->vm_mm && !is_vm_hugetlb_page(vma)) {
> memset(&mss, 0, sizeof(mss));
> walk_page_vma(vma, &smaps_walk);
> add_smaps_sum(&mss, &mss_sum);
> }
> }
> seq_printf(m,
> "Rss: %8lu kB\n"
> "Pss: %8lu kB\n"
> "Shared_Clean: %8lu kB\n"
> [...],
> mss_sum.resident >> 10,
> (unsigned long)(mss_sum.pss >> (10 + PSS_SHIFT)),
> mss_sum.shared_clean >> 10,
> [...]);
> [...]
> }
>


Thanks Jann for being really clear about this stuff. It is much appreciated!

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